为什么我的脚本的顺序给出了Divide by Zero错误？

Question

我正在进行一些初学Python练习。我有以下工作代码：

# Use the file name mbox-short.txt as the file name
fname = raw_input("Enter file name: ")
fh = open(fname)
inp=fh.readlines()
count=0
total=0.0
for line in inp:
    line=line.rstrip()
    if not line.startswith("X-DSPAM-Confidence:"): 
        continue
    value=line[19:]
    value=float(value)
    count=count+1   
    total=total + value
print "Average spam confidence:",total/count

当我第一次写这篇文章时，我把＆＃34;计数＆＃34; ＆＃34;值＆＃34;之前的行像这样的行：

# Use the file name mbox-short.txt as the file name
fname = raw_input("Enter file name: ")
fh = open(fname)
inp=fh.readlines()
count=0
total=0.0
for line in inp:
    line=line.rstrip()
    if not line.startswith("X-DSPAM-Confidence:"): 
        continue
    count=count+1           
    value=line[19:]
    value=float(value)
    total=total + value
print "Average spam confidence:",total/count

这导致零除错误。为什么呢？